华南理工大学：《食品分析》课程PPT教学课件（Food Analysis）Chapter 12 Reporting Results and Reliability of Analyses

LOGO Reporting Results and Reliability of Analyses introduce Reporting Results 3 Reliability.of Analyses

LOGO Reporting Results and Reliability of Analyses 1 2 Reporting Results 3 Reliability of Analyses introduce

LOGO Reporting Results and Reliability of Analyses The basic purpose of an analytical assay is to determine the mass (weight)of a component in a sample.The numerical result of the assay is expressed as a weight percentage or in other units that are equivalent to the mass/mass ratio.The mass (weight)of a component in a food sample is calculated from a determination of a parameter whose magnitude is a function of the mass of the specific component in the sample. Some properties are basically mass dependent.Absorption of light or other forms of radiant energy is a function of the number of molecules,atoms,or ions in the absorbing species.Although certain properties,such as specific gravity and refractive index,are not mass dependent,they can be used indirectly for mass determination. Thus,one can determine the concentration of ethanol in aqueous solutions by a density determination.Refractive index is used routinely to determine soluble solids(mainly sugars)in syrups and jams.Some mass-dependent properties may be characteristic of several or even of a single component and may be used for selective and specific assays.Examples are light absorption, polarization,or radioactivity.Some properties have both a

LOGO The basic purpose of an analytical assay is to determine the mass (weight) of a component in a sample. The numerical result of the assay is expressed as a weight percentage or in other units that are equivalent to the mass/mass ratio. The mass (weight) of a component in a food sample is calculated from a determination of a parameter whose magnitude is a function of the mass of the specific component in the sample. Some properties are basically mass dependent. Absorption of light or other forms of radiant energy is a function of the number of molecules, atoms, or ions in the absorbing species. Although certain properties, such as specific gravity and refractive index, are not mass dependent, they can be used indirectly for mass determination. Thus, one can determine the concentration of ethanol in aqueous solutions by a density determination. Refractive index is used routinely to determine soluble solids (mainly sugars) in syrups and jams. Some mass-dependent properties may be characteristic of several or even of a single component and may be used for selective and specific assays. Examples are light absorption, polarization, or radioactivity. Some properties have both a Reporting Results and Reliability of Analyses

LOGO magnitude and a specificity parameter(nuclear magnetic resonance and infrared spectroscopy).Such properties are of great analytical value because they provide selective determinations of a relatively large number of substances. In this chapter,we describe conventional ways of expressing analytical results and discuss the significance of specificity,accuracy. precision,and sensitivity in assessing the reliability of analyses. In recent years the metric SI system of units has gained worldwide acceptance.It has been recommended or required by International Union of Pure and Applied Chemistry(IUPAC),and the International Union of Pure and Applied Physics(TUPAP),as well as by an increasing number of scientific and professional organizations in the United States and by the industry and the trade.The SI system contains seven base units,two supplementary units,15 derived units having special names,and 14 prefixes for multiple and submultiple units.All physical properties can be quantified by 38 names

LOGO magnitude and a specificity parameter (nuclear magnetic resonance and infrared spectroscopy). Such properties are of great analytical value because they provide selective determinations of a relatively large number of substances. In this chapter, we describe conventional ways of expressing analytical results and discuss the significance of specificity, accuracy, precision, and sensitivity in assessing the reliability of analyses. In recent years the metric SI system of units has gained worldwide acceptance. It has been recommended or required by International Union of Pure and Applied Chemistry (IUPAC), and the International Union of Pure and Applied Physics (IUPAP), as well as by an increasing number of scientific and professional organizations in the United States and by the industry and the trade. The SI system contains seven base units, two supplementary units, 15 derived units having special names, and 14 prefixes for multiple and submultiple units. All physical properties can be quantified by 38 names

LOGO Reporting Results In reporting analytical results,both the reference basis and the units used to express the results must be considered.For example, analyses can be performed and the results reported on the edible portion only or on the whole food as purchased.Results can be reported on an as-is basis,on an air-dry basis,on a dry matter basis, or on an arbitrarily selected moisture basis (e.g.,14%in cereals). To convert contents(%)of component Y from oven-dried (OD)to an as-received(AR)basis,or vice versa,the following formulas are used: %Y= %Y×100 (100-%loss oD） %YAR= %Y(100-%loss oD） 100

LOGO In reporting analytical results, both the reference basis and the units used to express the results must be considered. For example, analyses can be performed and the results reported on the edible portion only or on the whole food as purchased. Results can be reported on an as-is basis, on an air-dry basis, on a dry matter basis, or on an arbitrarily selected moisture basis (e.g., 14% in cereals). To convert contents (%) of component Y from oven-dried (OD) to an as-received (AR) basis, or vice versa, the following formulas are used: Reporting Results (100 % ) % 100 % OD loss Y Y −  =

LOGO To convert contents from an as-received basis to an arbitrary moisture basis,the following formula is used: %Y= %YAR(100-arbitrarymoisture%) 100-%moisture Ar

LOGO To convert contents from an as-received basis to an arbitrary moisture basis, the following formula is used:

LOGO To weight out a sample on an arbitrary moisture(AM)basis,use the following: apie6gt抛 %dmater型Xrair9dsayplaeg drymatte

LOGO To weight out a sample on an arbitrary moisture (AM) basis, use the following:

LOGO To obtain dry matter,subtract percentage of moisture from 100. If the moisture has been determined in two stages,air drying followed by oven drying,compute total moisture contents of sample as follows: 7t=A+100-9B 100 Where TM is the total moisture,A the moisture loss in air drying,and B the%moisture of air-dried sample as determined by oven drying

LOGO To obtain % dry matter, subtract percentage of moisture from 100. If the moisture has been determined in two stages, air drying followed by oven drying, compute total moisture contents of sample as follows: Where TM is the % total moisture, A the % moisture loss in air drying, and B the % moisture of air-dried sample as determined by oven drying

LOGO Tables,nomograms,and calculators are available to simplify calculations in expressing results on a given basis,or for weighing samples on a fixed moisture basis(e.g.,20%in dried fruit).In view of the very wide range in moisture contents in various foods, analytical results are often meaningless unless the basis of expressing the results is known. Expressing analytical results on an as-is basis is wrought with many difficulties.It is practically impossible to eliminate considerable desiccation of fresh plant material.In some instances,even if great pains are taken to reduce such losses,the results may still vary widely.For example,the moisture contents of leafy foods may vary by as much as 10%depending on the time of harvest(from early morning to late afternoon).Similarly,the moisture contents of bread crust and crumb change from the moment bread is removed from the oven as a result of moisture migration and evaporation. Absorption of water in baked or roasted low-moisture foods (crackers,coffee)is quite substantial.In most cases,storing air- dried foods in hermetically closed containers is least

LOGO Tables, nomograms, and calculators are available to simplify calculations in expressing results on a given basis, or for weighing samples on a fixed moisture basis (e.g., 20% in dried fruit). In view of the very wide range in moisture contents in various foods, analytical results are often meaningless unless the basis of expressing the results is known. Expressing analytical results on an as-is basis is wrought with many difficulties. It is practically impossible to eliminate considerable desiccation of fresh plant material. In some instances, even if great pains are taken to reduce such losses, the results may still vary widely. For example, the moisture contents of leafy foods may vary by as much as 10% depending on the time of harvest (from early morning to late afternoon). Similarly, the moisture contents of bread crust and crumb change from the moment bread is removed from the oven as a result of moisture migration and evaporation. Absorption of water in baked or roasted low-moisture foods (crackers, coffee) is quite substantial. In most cases, storing air￾dried foods in hermetically closed containers is least

LOGO troublesome.Once the moisture contents of such foods are determined,samples can be used for analyses over a reasonable period. The concentrations of major components are generally expressed on a percentage by weight or percentage by volume basis.For liquids and beverages,g per 100mL is often reported.Minor components are calculated as mg (or mcg)per kg or L;vitamins in mcg or international units per 100g or 100mL.Amuunts of spray residues are often reported in ppm(parts per million). In calculating the protein contents of a food,it is generally assumed the protein contains 16%nitrogen.To convert from organic nitrogen(generally determined by the Kjeldahl method;see Chapter 37)to protein,the factor of 6.25=100/16 is used.In specific foods known to contain different concentrations of nitrogen in the protein, other conversion factors are used(5.7 in cereals,6.38 in milk). Heidelbaugh et al.(1975)compared three methods for calculating the protein content of 68 foods:(1)multiplication of Kjeldahl nitrogen by 6.25;(2)multiplication of Kjeldahl nitrogen by factors ranging

LOGO troublesome. Once the moisture contents of such foods are determined, samples can be used for analyses over a reasonable period. The concentrations of major components are generally expressed on a percentage by weight or percentage by volume basis. For liquids and beverages, g per 100mL is often reported. Minor components are calculated as mg (or mcg) per kg or L; vitamins in mcg or international units per 100g or 100mL.Amuunts of spray residues are often reported in ppm (parts per million). In calculating the protein contents of a food, it is generally assumed the protein contains 16% nitrogen. To convert from organic nitrogen (generally determined by the Kjeldahl method; see Chapter 37) to protein, the factor of 6.25=100/16 is used. In specific foods known to contain different concentrations of nitrogen in the protein, other conversion factors are used (5.7 in cereals, 6.38 in milk). Heidelbaugh et al. (1975) compared three methods for calculating the protein content of 68 foods: (1) multiplication of Kjeldahl nitrogen by 6.25; (2) multiplication of Kjeldahl nitrogen by factors ranging

LOGO from 5.30 to 6.38 depending on the type of food;and(3)calculation on the basis of amino acid composition,determined by chemical analyses.Up to 40%differences in protein content were found depending on the calculation method.There were,however,only small differences in mixed diets representing typical menus. If a food contains a mixture of carbohydrates,the sugars and starch are often expressed as dextrose.In lipid analyses(free fatty acids or total lipid contents)calculations are based on the assumption that oleic acid is the predominant component.Organic acids are calculated as citric,malic,lactic,or acetic acid depending on the main acid in the fruit or vegetable. Mineral components can be expressed on an as-is basis or as of total ash.In either case the results can be calculated as elements or as the highest valency oxide of the element. Amino acid composition can be expressed in several ways:g amino acid per 100 g of sample,or per 100 g of protein,or per 100 g of amino acids.For the determination of molar distribution of amino acids in protein,g-mol of amino acid residue per 100 g-mol of amino

LOGO from 5.30 to 6.38 depending on the type of food; and (3) calculation on the basis of amino acid composition, determined by chemical analyses. Up to 40% differences in protein content were found depending on the calculation method. There were, however, only small differences in mixed diets representing typical menus. If a food contains a mixture of carbohydrates, the sugars and starch are often expressed as dextrose. In lipid analyses (free fatty acids or total lipid contents) calculations are based on the assumption that oleic acid is the predominant component. Organic acids are calculated as citric, malic, lactic, or acetic acid depending on the main acid in the fruit or vegetable. Mineral components can be expressed on an as-is basis or as % of total ash. In either case the results can be calculated as elements or as the highest valency oxide of the element. Amino acid composition can be expressed in several ways: g amino acid per 100 g of sample, or per 100 g of protein, or per 100 g of amino acids. For the determination of molar distribution of amino acids in protein, g-mol of amino acid residue per 100 g-mol of amino